Two more presidential elections, in 2016 and 2020, will be contested under the current Electoral College configuration, which gave President Barack Obama a second term on Tuesday. This year’s results suggest that this could put Republicans at a structural disadvantage.

Based on a preliminary analysis of the returns, Mitt Romney might have had to win the national popular vote by 3 percentage points to be assured of winning the Electoral College. The last Republican to do that was George H.W. Bush, in 1988.

The FiveThirtyEight model had a very strong night Tuesday, but it was wrong about the identity of the tipping-point state — the state that would give the winner his 270th electoral vote. Based on the polls, it appeared that Ohio was the most likely to be the tipping point. Instead, it was Colorado — just as it was in 2008.

(The Electoral College tipping point can be determined by arranging the 50 states and the District of Columbia from the most Democratic to the most Republican, based on their preliminary results from Tuesday, and counting up the number of electoral votes for the Democratic candidate, starting at zero and going up to 538. Colorado was the state to carry the president over the 270 mark.)

The worry for Republicans is that Obama won Colorado by nearly 5 percentage points (4.7, to be precise). Obama’s margin in the national popular vote, as of this writing, is 2.4 percentage points. We estimate that it will grow to 2.5 percentage points, or perhaps slightly higher, once some remaining returns and provisional ballots are counted. But it seems clear that Obama had some margin to spare in the Electoral College.

Had the popular vote been a tie — assuming that the margin in each state shifted uniformly — he still would have won re-election with 285 electoral votes, carrying Colorado and Virginia, although losing Florida and Ohio.

In fact, had Romney won the popular vote by 2 percentage points, Obama still would have won the Electoral College, losing Virginia but holding on to Colorado.

Of course, the relative order of the states can shift a bit from election to election: In 2000, after all, it was Democrats who lost the Electoral College despite winning the popular vote.

Looking ahead, Ohio might be one of the Republicans’ lesser worries. Obama did win the state, but his margin is 1.9 percentage points based on the ballots in so far, slightly less than his margin of victory nationally, and he might have benefited there from the auto bailout, a one-off event.

But Obama did not need Ohio to carry the Electoral College. Instead, states where there have been demographic shifts, like Colorado, gave him enough of a cushion.

Nor was Ohio the only formerly Republican-leaning state to move closer to the Electoral College tipping point. Obama’s margins in Virginia, Florida and North Carolina also held up well compared with 2008.

Virginia, in fact, was slightly more Democratic-leaning than the country as a whole this year, voting for Obama by 3 percentage points.